The present invention relates to the field of telecommunication networks and more precisely to the field of the metrology of packet transmission telecommunication networks.
Metrology, in the literal sense of “science of measurement”, is expanding in different network fields such as traffic characterization and modeling, traffic analysis and quality of service and performance optimization. Network metrology is also used to improve network supervision. One particular objective is to provide assistance with the dimensioning of a network and with diagnosing problems detected in a network.
The increasing complexity of networks, and in particular of the Internet, leads to a lack of knowledge of traffic and conditions of use. It is becoming more and more difficult to have real control of the network and its behavior.
The traffic of a network is generally made up of a plurality of streams of packets. A stream of packets is defined as an exchange of data between two terminals of a network the packets whereof have common characteristics, in particular common source, destination and service characteristics.
Metrology generally has the objective of determining measurements to be performed on the traffic of the network under study in order to obtain a better knowledge of that traffic.
Two main types of measurements are known. A first type is made up of measurements performed on a stream of test packets. To perform these so-called “active” measurements, a stream of test packets is sent across the network being studied from a sender first terminal to a receiver second terminal. A test packet generally has a specific format containing a first field indicating a time reference of sending the packet and a second field indicating the sequence number of the packet in the stream of test packets sent. Consequently, the receiver terminal determines a transmission lead time of a test packet from the sender terminal as a function of the first field of the packet. The receiver terminal can also detect losses of packets as a function of the second field of a test packet. More generally, a test packet is a packet whereof a sending time reference is known and that can be distinguished from other packets on reception in order to associate it with an arrival time reference or to determine that it has been lost.
It is thus possible to obtain performance characteristics of an “end-to-end” stream, i.e. of the complete path of the stream of test packets, from the sender to the receiver, and in particular measurements of the transmission lead time between the two terminals, on the basis of the known sending and receiving time references of the packets.
This first type of measurement therefore produces performance measurements on a complete path of the stream of test packets, i.e. between the sender terminal of the stream and the receiver terminal of the stream. The measurements obtained in this way relate to the test packets of a stream. Because of this they are qualitatively accurate.
One drawback of this type of measurement is that it provides information relating only to the extremities of the stream of test packets. Thus it is impossible to obtain information on a segment of the complete path between two network equipments or between a network equipment and one of the terminals. Information obtained in this way is therefore geographically inaccurate.
There is known a second type of measurement performed in a network equipment by an analysis of the streams passing in transit through it. These so-called “passive” measurements can be performed either by onboard measurement units in the network equipments or by measurement units (or passive probes) external to the network equipments and dedicated to passive measurements. The latter generally have less information available than onboard measurement units. These measurement units monitor the traffic circulating on the links between the network equipments. This type of passive measurement, widely used in existing networks, produces volumetric information for each stream and for each network equipment.
One drawback of this type of measurement is that it supplies information relating to a network equipment that is very difficult to correlate with other information relating to another network equipment. Consequently, even though it is possible to obtain relatively accurate topological information on a given segment by correlation, such correlation remains complex to implement, in particular if the streams are sampled in order to analyze them.
Another drawback of this type of measurement is that it provides only volumetric information relating to the stream for each network equipment, in particular the number of analyzed packets and the sum of the sizes of the analyzed packets for a given stream. Consequently, the information obtained by this type of measurement may prove to be qualitatively insufficient and even somewhat unreliable, in particular if the streams are sampled in order to analyze them.
It is thus beneficial to obtain qualitatively accurate information, i.e. information relating to the packets of a stream, and geographically accurate information, i.e. information relating to segments of the complete path of the stream in the existing networks.
Note that the expression “network equipment” refers to an active network equipment, i.e. one that fulfills an active processing function in the network, such as switches or routers, for example. An active processing function in the network may also be defined as the opposite of a passive processing function fulfilled in particular by a measurement unit.